Coined by Carl Elefante, “the greenest building is…one that is already built,” is a familiar mantra for those at the intersection of preservation and sustainability. In 2025, Elefante who is a principal emeritus with Quinn Evans architects and past president of the American Institute of Architects, continued his groundbreaking work with the publication of Going for Zero: Decarbonizing the Built Environment on the Path to Our Urban Future. Informed by his decades of experience in architecture and preservation, the book delves into the ways in which buildings and cities can be a solution to the challenges faced by climate change.

Recently he spoke with National Trust Senior Policy Director Jim Lindberg about his new book and his ideas for how preservationists can help achieve a more sustainable, low-carbon future.

You’ve been spending a lot of time on the road recently, talking about your new book. Tell us about the evolution of the book and why you decided to do it.

Elefante: It's very directly the book of my professional experience and my perspectives as they relate to the challenges of the 21st century, with climate change being the one that is most urgent. My book is about understanding the challenges of climate change, but also the opportunities in responding to climate change. To decarbonize, we need to retool everything about the built environment, not just our habitation, but also transportation, agriculture, and industry. I wanted to highlight the opportunities and possibilities that come with that process.

Where do old buildings fit into a future that will need to accommodate so many more people and provide more affordable housing?

Elefante: We've forgotten the lessons about affordability from thousands of years of cities. Jane Jacobs talked about the power of older buildings. Affordability is a function of having older buildings in our cities that have already been paid for. The construction cost and land purchase have already been amortized.

Are there places where you see that kind of reinvestment happening?

Elefante: Toronto is an interesting place to look at despite having many problems like those in New York City. After World War II, Toronto built more than a thousand multi-story suburban apartment towers all around the city. Now those buildings are aging and in need of repair. In response, some architects in Toronto have begun a program to fix up these mid-century towers to keep them viable as affordable housing.

How can we make the case for reusing vernacular post-war structures that may not appear significant at first glance?

Elefante: This category of buildings still has value, including cultural value, even though many were not particularly great buildings even when first built. At Quinn Evans, we've converted some to residential use. Most often, these marginal mid-century buildings are stripped of their exterior cladding and gutted, keeping only the structural frame. In my book I defend even this radical approach to building reuse from a carbon standpoint as something that still has real climate benefits.

We’ve been working to make historic buildings more energy efficient for years. Now we also need to make the transition to carbon-free operations, which means electrification. How does this impact preservation?

Elefante: When buildings are powered with electricity alone, and when only renewable power-sources are used, operational greenhouse gas emissions are reduced to zero, period. While better envelope performance is preferable, many of the so-called problems of traditional buildings become much less crucial. In fact, many of the so-called advantages of modern-era construction are misnomers.

Simplistic benefits, like glazing with a higher insulation rating, can look very different when viewed from a life-cycle perspective. I have learned firsthand the importance of traditional materials with long service-life and repairability over so-called maintenance-free materials that end up in the landfill in a matter of a few decades. Built heritage has much to teach about long-term value and performance.

You are known for coining the phrase “the greenest building is…one that is already built.” How has this made an impact?

Elefante: That phrase was published in an article I wrote for the National Trust’s Forum Journal in 2007. To this day that journal article is quoted every week literally around the world—in dissertations and professional journals. In the preservation world, it's helped a lot of people understand that preservation contributes enormously to sustainability and climate action. Through my connection to Architecture 2030 I’ve seen how the goals of retaining and reusing existing buildings are gaining attention at the highest levels of international climate discussion. But there is still the idea that we’re going to make everything like modern buildings—with triple-glazed windows. Are we going to tear out windows that have stood the test of time and replace them with technology that we’ll throw in the landfill in 50 years? We need to be advocates for the long-term value of building materials and systems.

One of the quotes in your book is from Bill McDonough, who reflects on the differences between steamships and sailing ships from a sustainability perspective, noting the efficiencies and benefits of traditional practices. How do you apply that idea to buildings?

Elefante: We need to look hard at the climate standards that are used for building mechanical design. Last week I was at an ASHRAE (formerly American Society of Heating Refrigerating and Air-Conditioning Engineers) committee conference. I am happy to say that they were very interested in hearing a historic building perspective on comfort. Historic buildings were designed around occupant operability: they have windows and shutters and awnings and curtains that open and close. Modern practice is to seal up entire buildings and operate them at one temperature and humidity setting all year long. It requires energy use, and carbon pollution, regardless of exterior conditions. And medical science is beginning to understand how this simplistic idea about comfort affects our metabolism and health.

Does preservation practice need to change for us to help solve the challenges we face?

Elefante: Even the preservation world has a modern era bias to it. By that I mean that we're too often thinking of buildings as artifacts, preserving buildings to a former glory they never had. They're not ceramics displayed on a shelf. They have to work for a new generation of users during a new era with different demands. Buildings have always adapted over time, over centuries. Go to Rome, go anywhere where you can see centuries of living. People have adapted buildings to make them useful, livable and comfortable generation after generation. That is what it means to live in buildings. We have to allow them to change, not freeze buildings in amber.